1. Field of Invention
The present invention relates generally to propulsors for submersible vehicles and, more particularly, to a torque balanced postswirl propulsor unit for a submersible vehicle and a method for eliminating operational torque on a submersible vehicle.
2. Brief Description of Related Art
An operating problem associated with submersible vehicles, particularly small vehicles such as torpedoes and remotely controlled or autonomous underwater vehicles, is maintaining operational stability, specifically roll stability, while being propelled by a rotating propulsor. Roll stability (zero roll underway) can be accomplished if the vehicle achieves a torque balance under operating conditions. Moreover, submersible vehicles having small maximum transverse dimensions, e.g., hullforms comprising small-diameter bodies of revolution having small maximum diameters, can dedicate only limited internal volume to propulsion machinery. Additionally, for small submersible vehicles, the installed power available for propulsion is limited by machinery weight and volume considerations, thus, necessitating the minimizing of propulsion machinery weight and volume.
Conventional single rotation (SR) propellers have simple machinery arrangements that occupy limited internal volume. However, SR propulsors are incapable of providing torque balance to the vehicle. Consequently, large control surfaces are required to maintain roll stability. However, large control surfaces significantly increase the resistance and, thus, decrease the speed-power performance of the vehicle.
Contrarotating (CR) propellers can, in some cases, achieve torque balance. However, CR propellers require complex shafting and gearing arrangements that add weight and occupy large amounts of internal space. Consequently, in spite of the hydrodynamic benefits of CR propellers, complex shafting and gearing arrangements have restricted the application of CR propulsors in small vehicles.
Thus, there is a need to provide a propulsor that provides torque balance for enhanced stability and improved performance to submersible vehicle of all sizes. More particularly, there is a need to provide a propulsor for small submersible vehicles that both incorporates a simple, small, lightweight machinery arrangement and provides vehicle stability enhancement.